Microbial inhibiting compositions and their use

ABSTRACT

A biocidal composition and method for inhibiting and controlling the growth of the fungus, Trichoderma viride, are disclosed. The composition comprises an amount, effective for the intended purpose of diiodomethyl-p-tolylsulfone and an additional biocidal component. The method comprises administering between about 0.1 to about 200 parts of this combined treatment (based on one million parts of the desired aqueous system) to the particular water containing system for which treatment is desired.

This a is a divisional of application Ser. No. 08/038,583 filed Mar. 26, 1993, U.S. Pat. No. 5,292,776.

BACKGROUND OF THE INVENTION

The present invention relates to methods for controlling the growth of microbes in an aqueous system. More particularly, it relates to methods of microbial inhibition which entail adding to the system compositions comprising diiodomethyl-p-tolylsulfone (DIMPS) and at least one other component, the composition exhibiting synergy.

The formation of slimes by microorganisms is a problem that is encountered in many aqueous systems. For example, the problem is not only found in natural waters such as lagoons, lakes, ponds, etc., and confined waters as in pools, but also in such industrial systems as cooling water systems, air washer systems and pulp and paper mill systems. All possess conditions which are conducive to the growth and reproduction of slime-forming microorganisms. In both once-through and recirculating cooling systems, for example, which employ large quantities of water as a cooling medium, the formation of slime by microorganisms is an extensive and constant problem.

Airborne organisms are readily entrained in the water from cooling towers and find this warm medium an ideal environment for growth and multiplication. Aerobic and heliotropic organisms flourish on the tower proper while other organisms colonize and grow in such areas as the tower sump and the piping and passages of the cooling system. The slime formation not only aids in the deterioration of the tower structure in the case of wooden towers, but also promotes corrosion when it deposits on metal surfaces. Slime carried through the cooling system plugs and fouls lines, valves, strainers, etc., and deposits on heat exchange surfaces. In the latter case, the impedance of heat transfer can greatly reduce the efficiency of the cooling system.

In pulp and paper mill systems, slime formed by microorganisms is commonly encountered and causes fouling, plugging, or corrosion of the system. The slime also becomes entrained in the paper produced to cause breakouts on the paper machines which results in work stoppages and the loss of production time. The slime is also responsible for unsightly blemishes in the final product, which result in rejects and wasted output.

The previously discussed problems have resulted in the extensive utilization of biocides in cooling water and pulp and paper mill systems. Materials which have enjoyed widespread use in such applications include chlorine, chlorinated phenols, organo-bromines, and various organo-sulfur compounds. All of these compounds are generally useful for this purpose but each is attended by a variety of impediments. For example, chlorination is limited both by its specific toxicity for slime-forming organisms at economic levels and by the tendency of chlorine to react, which results in the expenditure of the chlorine before its full biocidal function is achieved.

Other biocides are attended by odor problems and hazards with respect to storage, use or handling which limit their utility. To date, no one compound or type of compound has achieved a clearly established predominance with respect to the applications discussed. Likewise, lagoons, ponds, lakes, and even pools, either used for pleasure purposes or used for industrial purposes for the disposal and storage of industrial wastes, become, during the warm weather, besieged by slime due to microorganism growth and reproduction. In the case of industrial storage or disposal of industrial materials, the microorganisms cause additional problems which must be eliminated prior to the use of the materials or disposal of the waste.

Naturally, economy is a major consideration with respect to all of these biocides. Such economic considerations attach to both the cost of the biocide and the expense of its application. The cost performance index of any biocide is derived from the basic cost of the material, its effectiveness per unit of weight, the duration of its biocidal or biostatic effect in the system treated, and the ease and frequency of its addition to the system treated. To date, none of the commercially available biocides has exhibited a prolonged biocidal effect. Instead, their effectiveness is rapidly reduced as a result of exposure to physical conditions such as temperature, association with ingredients contained by the system toward which they exhibit an affinity or substantivity, or the like, with a resultant restriction or elimination of their biocidal effectiveness, or by dilution.

As a consequence, the use of such biocides involves their continuous or frequent addition to systems to be treated and their addition to multiple points or zones in the systems to be treated. Accordingly, the cost of the biocide and the labor cost of applying it are considerable. In other instances, the difficulty of access to the zone in which slime formation is experienced precludes the effective use of a biocide. For example, if in a particular system there is no access to an area at which slime formation occurs the biocide can only be applied at a point which is upstream in the flow system. However, the physical or chemical conditions, e.g., chemical reactivity, thermal degradation, which exist between the point at which the biocide may be added to the system and the point at which its biocidal effect is desired render the effective use of a biocide impossible.

Similarly, in a system experiencing relatively slow flow, such as a paper mill, if a biocide is added at the beginning of the system, its biocidal effect may be completely dissipated before it has reached all of the points at which this effect is desired or required. As a consequence, the biocide must be added at multiple points, and even then a diminishing biocidal effect will be experienced between one point of addition to the system and the next point downstream at which the biocides may be added. In addition to the increased cost of utilizing and maintaining multiple feed points, gross ineconomies with respect to the cost of the biocide are experienced. Specifically, at each point of addition, an excess of the biocide is added to the system in order to compensate for that portion of the biocide which will be expended in reacting with other constituents present in the system or experience physical changes which impair its biocidal activity.

It has been found possible to provide a fungicidal or biocidal composition which comprises, as active ingredients, diiodomethyl-p-tolylsulfone and at least one additional chemical component. The additional component may be:

1) 2-bromo-2-nitropropane-1,3-diol (BNPD),

2) sodium 2-pyridinethiol-1-oxide (PEO), or

3) 2-(thiocyano-methyl thio) benzothiazole (TCMTB).

Surprisingly, it has been found that mixtures of diiodomethyl-p-tolylsulfone with any of the additional biocidal components listed are especially efficacious in controlling the growth of fungal microbes, specifically the Trichoderma viride species. This particular species is a common nuisance fungal type found in industrial cooling waters and pulping and papermaking systems.

This particular species of mold is a member of the Fungi Imperfecti which reproduce by means of asexual spores or fragmentation of mycelium. It is commonly found on fallen timber and is a widely occurring soil organism. Because of its ubiquitous nature, this mold continually contaminates open cooling systems and pulping and papermaking systems. Contamination can take the form of airborne spores or fungal mats--a mass of agglomerated hyphae bound together with bacterial cells and cemented by gelatinous polysaccharide or proteinaceous material. The slimy mass entraps other detritus, restricts water flow and heat transfer and may serve as a site for corrosion.

These fungi are able to grow in environments hostile to other lifeforms. While they are strict aerobes, Trichoderma produce both hyphae, the vegetative structure, and spores which require minimal metabolic turnover and are able to withstand harsher environmental conditions. Accordingly, by reason of demonstrated efficacy in the growth inhibition of this particular species, one can expect similar growth inhibition attributes when other fungi are encountered. It is also expected that these compositions will exhibit similar growth inhibition attributes when bacterial and algal species are encountered.

According to the present invention there is provided a method for controlling the growth of fungi, particularly Trichoderma viride fungi, in an aqueous system, which comprises adding to the system from about 0.1 to 200 parts by weight of the aqueous system, of a composition comprising a synergistic mixture of (a) diiodomethyl-p-tolylsulfone and (b) at least one additional biocidal component selected from (1) to (3) as hereinbefore defined. The aqueous system may comprise, for example, a cooling water system or a pulping and papermaking system.

In accordance with the present invention, the combined treatment of diiodomethyl-p-tolylsulfone with any one of the additional biocidal components may be added to the desired aqueous system in need of biocidal treatment, in an amount of from about 0.1 to about 200 parts of the combined treatment to one million parts (by weight) of the aqueous medium. Preferably, about 5 to about 50 parts of the combined treatment per one million parts (by weight) of the aqueous medium is added.

The combined treatments are added, for example, to cooling water systems, paper and pulp mill systems, pools, ponds, lagoons, or lakes, to control the formation of fungal microorganisms, which may be contained by, or which may become entrained in, the system to be treated. It has been found that the compositions and methods of utilization of the treatments are efficacious in controlling the fungal organism, Trichoderma viride, which may populate these systems. It is thought that the combined treatment compositions and methods of the present invention will also be efficacious in inhibiting and controlling all types of aerobic microorganisms.

Surprisingly, it has been found that when the ingredients are mixed, in certain instances, the resulting mixtures possess a higher degree of fungicidal activity than that of the individual ingredients comprising the mixtures. Accordingly, it is possible to produce highly efficacious biocides. Because of the enhanced activity of the mixtures, the total quantity of the biocidal treatments may be reduced. In addition, the high degree of biocidal effectiveness which is provided by each of the ingredients may be exploited without use of higher concentrations of each.

The following experimental data were developed. It is to be remembered that the following examples are to be regarded solely as being illustrative, and not as restricting the scope of the invention.

Diiodomethyl-p-tolylsulfone and an additional biocidal component were added in varying ratios and over a wide range of concentrations to a liquid nutrient medium which was subsequently inoculated with a standard volume of a suspension of the spores from Trichoderma viride. Growth was measured by determining the amount of radioactivity accumulated by the cells when 14C-glucose was added as the sole source of carbon in the nutrient medium. The effect of the biocide chemicals, alone and in combination, is to reduce the rate and amount of 14C incorporation into the cells during incubation, as compared to controls not treated with the chemicals. Additions of the biocides, alone and in varying combinations and concentrations, were made according to the accepted "checkerboard" technique described by M. T. Kelley and J. M. Matsen, Antimicrobial Agents and Chemotherapy. 9:440 (1976). Following a two hour incubation, the amount of radioactivity incorporated in the cells was determined by counting (14C liquid scintillation procedures) for all treated and untreated samples. The percent reduction of each treated sample was calculated from the relationship: ##EQU1##

Plotting the % reduction of 14C level against the concentration of each biocide acting alone results in a dose-response curve, from which the biocide dose necessary to achieve any given % reduction can be interpolated.

Synergism was determined by the method of calculation described by F. C. Kull, P. C. Eisman, H. D. Sylwestrowicz and R. L. Mayer, Applied Microbiology 9,538 (1961) using the relationship: ##EQU2## where: ^(Q) a=quantity of compound A, acting alone, producing an end point

^(Q) b=quantity of compound B, acting alone, producing an end point

^(Q) A=quantity of compound A in mixture, producing an end point

^(Q) B=quantity of compound B in mixture, producing an end point

The end point used in the calculations is the % reduction caused by each mixture of A and B. ^(Q) A and ^(Q) B are the individual concentrations in the A/B mixture causing a given % reduction. ^(Q) a and ^(Q) b are determined by interpolation from the respective dose-response curves of A and B as those concentrations of A and B acting alone which produce the same % reduction as each specific mixture produced.

Dose-response curves for each active acting alone were determined by linear regression analysis of the dose-response data. Data were fitted to a curve represented by the equation shown with each data set. After linearizing the data, the contributions of each biocide component in the biocide mixtures to the inhibition of radioisotope uptake were determined by interpolation with the dose-response curve of the respective biocide. If, for example, quantities of ^(Q) A plus ^(Q) B are sufficient to give a 50% reduction in 14C content, ^(Q) a and ^(Q) b are those quantities of A or B acting alone, respectively, found to give 50% reduction in 14C content. A synergism index (SI) is calculated for each combination of A and B.

Where the SI is less than 1, synergism exists. Where the SI=1, additivity exists. Where the SI is greater than 1, antagonism exists.

The data in the following tables come from treating Trichoderma viride, a common nuisance fungal type found in industrial cooling waters and in pulping and paper making systems, with varying ratios and concentrations of diiodomethyl-p-tolylsulfone and each additional biocidal component. Shown for each combination is the reduction of 14C content (% I), the calculated SI, and the weight ratio of diiodomethyl-p-tolylsulfone and each additional biocidal component.

                  TABLE I                                                          ______________________________________                                         DIMPS vs. BNPD                                                                 ppm     ppm       Ratio                                                        DIMPS.sup.1                                                                            BNPD.sup.2                                                                               DIMPS:BNPD   % I    SI                                       ______________________________________                                         6       0         100:0        88                                              3       0         100:0        76                                              1.5     0         100:0        48                                              0.75    0         100:0        28                                              0.38    0         100:0        20                                              0.19    0         100:0        12                                              0       1200      0:100        80                                              0       600       0:100        73                                              0       300       0:100        60                                              0       150       0:100        42                                              0       75        0:100        29                                              0       37.5      0:100        19                                              6       1200      1:200        92     1.53                                     3       1200      1:400        89     1.27                                     1.5     1200      1:800        76     1.96                                     0.75    1200      1:1600       82     1.26                                     0.38    1200      1:3158       81     1.25                                     0.19    1200      1:6316       49     6.10                                     6       600       1:100        91     1.22                                     3       600       1:200        87     0.95                                     1.5     600       1:400        88     0.94*                                    0.75    600       1:800        77     0.90*                                    0.38    600       1:1600       75     0.92*                                    0.19    600       1:3158       35     6.62                                     6       300       1:50         91     1.06                                     3       300       1:100        85     0.79*                                    1.5     300       1:200        76     0.80*                                    0.75    300       1:400        70     0.78*                                    0.38    300       1:800        66     0.81*                                    0.19    300       1:1600       28     5.05                                     6       150       1:25         91     0.97                                     3       150       1:50         86     0.67*                                    1.5     150       1:100        74     0.66*                                    0.75    150       1:200        64     0.68*                                    0.38    150       1:400        82     0.22*                                    0.19    150       1:800        56     0.63*                                    6       75        1:12.5       92     0.91*                                    3       75        1:25         85     0.64*                                    1.5     75        1:50         69     0.67*                                    0.75    75        1:100        52     0.85*                                    0.38    75        1:200        73     0.22*                                    0.19    75        1:400        41     0.78*                                    6       37.5      1:6.25       91     0.92*                                    3       37.5      1:12.5       83     0.65*                                    1.5     37.5      1:25         63     0.80*                                    0.75    37.5      1:50         40     1.17                                     0.38    37.5      1:100        62     0.28*                                    0.19    37.5      1:200        33     0.72*                                    ______________________________________                                          .sup.1 product containing 40% actives DIMPS                                    .sup.2 product containing 95% actives BNPD                               

                  TABLE II                                                         ______________________________________                                         DIMPS vs. BNPD                                                                 ppm     ppm       Ratio                                                        DIMPS.sup.1                                                                            BNPD.sup.2                                                                               DIMPS:BNPD   % I    SI                                       ______________________________________                                         6       0         100:0        91                                              3       0         100:0        81                                              1.5     0         100:0        59                                              0.75    0         100:0        26                                              0.38    0         100:0         0                                              0.19    0         100:0         0                                              0       1200      0:100        81                                              0       600       0:100        71                                              0       300       0:100        56                                              0       150       0:100        38                                              0       75        0:100        22                                              0       37.5      0:100         6                                              6       1200      1:200        95     1.72                                     3       1200      1:400        91     1.38                                     1.5     1200      1:800        87     1.24                                     0.75    1200      1:1600       84     1.23                                     0.38    1200      1:3158       82     1.22                                     0.19    1200      1:6316       82     1.18                                     6       600       1:100        94     1.43                                     3       600       1:200        90     1.04                                     1.5     600       1:400        83     0.94*                                    0.75    600       1:800        78     0.89*                                    0.38    600       1:1600       74     0.94*                                    0.19    600       1:3158       72     0.96                                     6       300       1:50         94     1.30                                     3       300       1:100        88     0.89*                                    1.5     300       1:200        79     0.76*                                    0.75    300       1:400        73     0.69*                                    0.38    300       1:800        65     0.76*                                    0.19    300       1:1600       60     0.87*                                    6       150       1:25         93     1.24                                     3       150       1:50         87     0.83*                                    1.5     150       1:100        77     0.66*                                    0.75    150       1:200        67     0.60*                                    0.38    150       1:400        56     0.69*                                    0.19    150       1:800        44     0.93*                                    6       75        1:12.5       94     1.18                                     3       75        1:25         88     0.77*                                    1.5     75        1:50         76     0.59*                                    0.75    75        1:100        59     0.62*                                    0.38    75        1:200        38     0.89*                                    0.19    75        1:400        21     1.39                                     6       37.5      1:6.25       93     1.19                                     3       37.5      1:12.5       86     0.76*                                    1.5     37.5      1:25         73     0.60*                                    0.75    37.5      1:50         48     0.76*                                    0.38    37.5      1:100        22     1.20                                     0.19    37.5      1:200        11     1.32                                     ______________________________________                                          .sup.1 product containing 40% actives DIMPS                                    .sup.2 product containing 95% actives BNPD                               

                  TABLE III                                                        ______________________________________                                         DIMPS vs. PEO                                                                  ppm     ppm       Ratio                                                        DIMPS.sup.1                                                                            PEO.sup.2 DIMPS:PEO    % I    SI                                       ______________________________________                                         6       0         100:0        85                                              3       0         100:0        77                                              1.5     0         100:0        58                                              0.75    0         100:0        38                                              0.38    0         100:0        29                                              0.19    0         100:0        25                                              0       80,000    0:100        91                                              0       40,000    0:100        86                                              0       20,000    0:100        80                                              0       10,000    0:100        66                                              0       5,000     0:100        48                                              0       2,500     0:100        47                                              6       80,000    1:13,333     92     2.07                                     3       80,000    1:26,666     91     1.79                                     1.5     80,000    1:53,333     91     1.60                                     0.75    80,000    1:106,666    90     1.56                                     0.38    80,000    1:280,701    90     1.52                                     0.19    80,000    1:421,052    90     1.51                                     6       40,000    1:6,666      92     1.44                                     3       40,000    1:13,333     89     1.21                                     1.5     40,000    1:26,666     88     1.11                                     0.75    40,000    1:53,333     86     1.09                                     0.38    40,000    1:105,263    86     1.06                                     0.19    40,000    1:210,526    85     1.04                                     6       20,000    1:3,333      91     1.12                                     3       20,000    1:6,666      89     0.82*                                    1.5     20,000    1:13,333     84     0.84*                                    0.75    20,000    1:26,666     78     0.98                                     0.38    20,000    1:52,631     76     1.13                                     0.19    20,000    1:105,263    72     1.25                                     6       10,000    1:1,666      91     0.98                                     3       10,000    1:3,333      87     0.70*                                    1.5     10,000    1:6,666      82     0.63*                                    0.75    10,000    1:13,333     68     1.10                                     0.38    10,000    1:26,315     61     1.47                                     0.19    10,000    1:52,631     58     1.68                                     6       5,000     1:833        90     0.91*                                    3       5,000     1:1,666      88     0.56*                                    1.5     5,000     1:3,333      81     0.47*                                    0.75    5,000     1:6,666      63     0.97                                     0.38    5,000     1:13,157     53     1.36                                     0.19    5,000     1:26,315     50     1.49                                     6       2,500     1:417        91     0.83*                                    3       2,500     1:833        89     0.49*                                    1.5     2,500     1:1666       82     0.39*                                    0.75    2,500     1:3,333      61     0.74*                                    0.38    2,500     1:6,579      50     1.03                                     0.19    2,500     1:13,158     47     0.97                                     ______________________________________                                          .sup.1 product containing 40% actives DIMPS                                    .sup.2 product containing 40% actives PEO                                

                  TABLE IV                                                         ______________________________________                                         DIMPS vs. PEO                                                                  ppm     ppm       Ratio                                                        DIMPS.sup.1                                                                            PEO.sup.2 DIMPS:PEO    % I    SI                                       ______________________________________                                         6       0         100:0        81                                              3       0         100:0        71                                              1.5     0         100:0        58                                              0.75    0         100:0        37                                              0.38    0         100:0        19                                              0.19    0         100:0        13                                              0       80,000    0:100        90                                              0       40,000    0:100        86                                              0       20,000    0:100        75                                              0       10,000    0:100        58                                              0       5,000     0:100        48                                              0       2,500     0:100        45                                              6       80,000    1:13,333     94     1.58                                     3       80,000    1:26,666     94     1.30                                     1.5     80,000    1:53,333     93     1.22                                     0.75    80,000    1:106,666    92     1.18                                     0.38    80,000    1:280,701    92     1.12                                     0.19    80,000    1:421,052    92     1.12                                     6       40,000    1:6,666      93     1.19                                     3       40,000    1:13,333     91     0.95*                                    1.5     40,000    1:26,666     90     0.83*                                    0.75    40,000    1:53,333     89     0.77*                                    0.38    40,000    1:105,263    88     0.74*                                    0.19    40,000    1:210,526    88     0.75*                                    6       20,000    1:3,333      92     0.95*                                    3       20,000    1:6,666      91     0.66*                                    1.5     20,000    1:13,333     86     0.64*                                    0.75    20,000    1:26,666     82     0.65*                                    0.38    20,000    1:52,631     80     0.66*                                    0.19    20,000    1:105,263    79     0.68*                                    6       10,000    1:1,666      90     0.91*                                    3       10,000    1:3,333      89     0.55*                                    1.5     10,000    1:6,666      81     0.55*                                    0.75    10,000    1:13,333     78     0.50*                                    0.38    10,000    1:26,315     75     0.52*                                    0.19    10,000    1:52,631     64     0.96                                     6       5,000     1:833        90     0.86*                                    3       5,000     1:1,666      87     0.54*                                    1.5     5,000     1:3,333      83     0.38*                                    0.75    5,000     1:6,666      72     0.46*                                    0.38    5.000     1:13,157     65     0.56*                                    0.19    5,000     1:26,315     48     1.39                                     6       2,500     1:417        88     0.86*                                    3       2.500     1:833        87     0.49*                                    1.5     2,500     1:1666       79     0.40*                                    0.75    2,500     1:3,333      62     0.59*                                    0.38    2,500     1:6,579      48     0.96                                     0.19    2,500     1:13,158     46     0.87*                                    ______________________________________                                          .sup.1 product containing 40% actives DIMPS                                    .sup.2 product containing 40% actives PEO                                

                  TABLE V                                                          ______________________________________                                         DIMPS vs. PEO                                                                  ppm     ppm       Ratio                                                        DIMPS.sup.1                                                                            PEO.sup.2 DIMPS:PEO    % I    SI                                       ______________________________________                                         6       0         100:0        81                                              3       0         100:0        74                                              1.5     0         100:0        55                                              0.75    0         100:0        27                                              0.38    0         100:0         6                                              0.19    0         100:0         0                                              0       80,000    0:100        88                                              0       40,000    0:100        86                                              0       20,000    0:100        77                                              0       10,000    0:100        61                                              0       5,000     0:100        50                                              0       2,500     0:100        43                                              6       80,000    1:13,333     91     2.07                                     3       80,000    1:26,666     90     1.72                                     1.5     80,000    1:53,333     89     1.62                                     0.75    80,000    1:106,666    86     1.71                                     0.38    80,000    1:280,701    88     1.52                                     0.19    80,000    1:421,052    88     1.49                                     6       40,000    1:6,666      89     1.63                                     3       40,000    1:13,333     88     1.22                                     1.5     40,000    1:26,666     85     1.14                                     0.75    40,000    1:53,333     89     0.99                                     0.38    40,000    1:105,263    83     1.07                                     0.19    40,000    1:210,526    83     1.08                                     6       20,000    1:3,333      89     1.31                                     3       20,000    1:6,666      88     0.86*                                    1.5     20,000    1:13,333     83     0.79*                                    0.75    20,000    1:26,666     77     0.91*                                    0.38    20,000    1:52,631     75     0.95*                                    0.19    20,000    1:105,263    73     1.01                                     6       10,000    1:1,666      87     1.21                                     3       10,000    1:3,333      86     0.74*                                    1.5     10,000    1:6,666      82     0.57*                                    0.75    10,000    1:13,333     71     0.77*                                    0.38    10,000    1:26,315     67     0.88*                                    0.19    10,000    1:52,631     65     0.89*                                    6       5,000     1:833        87     1.13                                     3       5,000     1:1,666      86     0.65*                                    1.5     5,000     1:3,333      82     0.44*                                    0.75    5,000     1:6,666      69     0.57*                                    0.38    5.000     1:13,157     61     0.70*                                    0.19    5,000     1:26,315     60     0.65*                                    6       2,500     1:417        87     1.07                                     3       2.500     1:833        85     0.62*                                    1.5     2,500     1:1666       79     0.48*                                    0.75    2,500     1:3,333      59     0.68*                                    0.38    2,500     1:6,579      45     1.11                                     0.19    2,500     1:13,158     45     0.94*                                    ______________________________________                                          .sup.1 product containing 40% actives DIMPS                                    .sup.2 product containing 40% actives PEO                                

                  TABLE VI                                                         ______________________________________                                         DIMPS vs. TCMTB                                                                ppm     ppm       Ratio                                                        DIMPS.sup.1                                                                            TCMTB.sup.2                                                                              DIMPS:TCMTB   % I   SI                                       ______________________________________                                         6       0         100:0         87                                             3       0         100:0         69                                             1.5     0         100:0         41                                             0.75    0         100:0         16                                             0.38    0         100:0          7                                             0.19    0         100:0          3                                             0       30        0:100         91                                             0       15        0:100         87                                             0       7.50      0:100         75                                             0       3.75      0:100         61                                             0       1.87      0:100         46                                             0       0.93      0:100         25                                             6       30        1:5.00        96    1.81                                     3       30        1:10.00       95    1.56                                     1.5     30        1:20.0        93    1.50                                     0.75    30        1:40.0        92    1.51                                     0.38    30        1:78.95       91    1.55                                     0.19    30        1:157.89      91    1.54                                     6       15        1:2.5         93    1.43                                     3       15        1:5.00        91    1.18                                     1.5     15        1:10.0        88    1.09                                     0.75    15        1:20.0        86    1.06                                     0.38    15        1:39.47       86    0.99                                     0.19    15        1:78.95       87    0.94*                                    6       7.50      1:1.25        90    1.23                                     3       7.50      1:2.50        85    1.02                                     1.5     7.50      1:5.00        79    1.00                                     0.75    7.50      1:10.0        76    0.98                                     0.38    7.50      1:19.74       74    0.95*                                    0.19    7.50      1:39.47       75    0.89*                                    6       3.75      1.60:1        89    1.08                                     3       3.75      1:1.25        82    0.85*                                    1.5     3.75      1:2.50        70    0.96                                     0.75    3.75      1:5.00        64    0.99                                     0.38    3.75      1:9.87        62    0.93*                                    0.19    3.75      1:19.74       62    0.88*                                    6       1.87      3.21:1        89    0.98                                     3       1.87      1.60:1        81    0.73*                                    1.5     1.87      1:1.25        62    0.99                                     0.75    1.87      1:2.49        52    1.06                                     0.38    1.87      1:4.92        49    1.00                                     0.19    1.87      1:9.84        43    1.16                                     6       0.93      6.45:1        90    0.90*                                    3       0.93      3.23:1        80    0.67*                                    1.5     0.93      1.61:1        50    1.24                                     0.75    0.93      1:1.24        37    1.42                                     0.38    0.93      1:2.45        30    1.40                                     0.19    0.93      1:4.89        29    1.26                                     ______________________________________                                          .sup.1 product containing 40% actives DIMPS                                    .sup.2 product containing 80% actives TCMTB                              

                  TABLE VII                                                        ______________________________________                                         DIMPS vs. TCMTB                                                                ppm     ppm       Ratio                                                        DIMPS.sup.1                                                                            TCMTB.sup.2                                                                              DIMPS:TCMTB   % I   SI                                       ______________________________________                                         6       0         100:0         87                                             3       0         100:0         77                                             1.5     0         100:0         49                                             0.75    0         100:0         21                                             0.38    0         100:0          5                                             0.19    0         100:0          0                                             0       25        0:100         92                                             0       12.50     0:100         84                                             0       6.25      0:100         73                                             0       3.13      0:100         59                                             0       1.56      0:100         41                                             0       0.78      0:100         21                                             6       25        1:4.17        96    1.92                                     3       25        1:8.33        94    1.63                                     1.5     25        1:16.67       93    1.53                                     0.75    25        1:33.33       92    1.47                                     0.38    25        1:65.79       91    1.48                                     0.19    25        1:131.58      91    1.41                                     6       12.5      1:2.08        93    1.53                                     3       12.5      1:4.17        89    1.27                                     1.5     12.5      1:8.33        86    1.18                                     0.75    12.5      1:16.67       85    1.10                                     0.38    12.5      1:32.90       85    1.02                                     0.19    12.5      1:65.79       85    0.96                                     6       6.25      1:1.04        91    1.33                                     3       6.25      1:2.08        84    1.11                                     1.5     6.25      1:4.17        75    1.19                                     0.75    6.25      1:8.33        74    1.01                                     0.38    6.25      1:16.45       73    0.94*                                    0.19    6.25      1:32.89       75    0.79*                                    6       3.13      1.9:1         89    1.21                                     3       3.13      1:1.04        81    0.95*                                    1.5     3.13      1:2.09        69    1.00                                     0.75    3.13      1:4.17        63    0.98                                     0.38    3.13      1:8.2         63    0.84*                                    0.19    3.13      1:16.47       60    0.86*                                    6       1.56      3.8:1         90    1.10                                     3       1.56      1.9:1         81    0.81*                                    1.5     1.56      1:1.04        62    1.00                                     0.75    1.56      1:2.08        48    1.23                                     0.38    1.56      1:4.10        45    1.10                                     0.19    1.56      1:8.21        36    1.43                                     6       0.78      7.69:1        89    1.07                                     3       0.78      3.85:1        80    0.78*                                    1.5     0.78      1.92:1        59    0.92*                                    0.75    0.78      1:1.04        40    1.22                                     0.38    0.78      1:2.05        32    1.20                                     0.19    0.78      1:4.10        24    1.35                                     ______________________________________                                          .sup.1 Product containing 40% actives DIMPS                                    .sup.2 Product containing 80% actives TCMTB                              

                  TABLE VIII                                                       ______________________________________                                         DIMPS vs. TCMTB                                                                ppm     ppm       Ratio                                                        DIMPS.sup.1                                                                            TCMTB.sup.2                                                                              DIMPS:TCMTB   % I   SI                                       ______________________________________                                         6       0         100:0         88                                             3       0         100:0         65                                             1.5     0         100:0         41                                             0.75    0         100:0         24                                             0.38    0         100:0         12                                             0.19    0         100:0          8                                             0       25        0:100         89                                             0       12.50     0:100         79                                             0       6.25      0:100         60                                             0       3.13      0:100         41                                             0       1.56      0:100         29                                             0       0.78      0:100         17                                             6       25        1:4.17        95    1.43                                     3       25        1:8.33        93    1.24                                     1.5     25        1:16.67       91    1.15                                     0.75    25        1:33.33       90    1.10                                     0.38    25        1:65.79       89    1.10                                     0.19    25        1:131.58      89    1.08                                     6       12.5      1:2.08        92    1.15                                     3       12.5      1:4.17        86    1.05                                     1.5     12.5      1:8.33        83    0.96                                     0.75    12.5      1:16.67       81    0.92*                                    0.38    12.5      1:32.90       79    0.90*                                    0.19    12.5      1:65.79       80    0.85*                                    6       6.25      1:1.04        90    1.02                                     3       6.25      1:2.08        79    0.99                                     1.5     6.25      1:4.17        68    1.14                                     0.75    6.25      1:8.33        64    1.10                                     0.38    6.25      1:16.45       60    1.16                                     0.19    6.25      1:32.89       58    1.17                                     6       3.13      1.9:1         90    0.88*                                    3       3.13      1:1.04        76    0.89*                                    1.5     3.13      1:2.09        60    1.15                                     0.75    3.13      1:4.17        52    1.14                                     0.38    3.13      1:8.2         45    1.26                                     0.19    3.13      1:16.47       42    1.31                                     6       1.56      3.8:1         91    0.80*                                    3       1.56      1:0.52        75    0.81*                                    1.5     1.56      1:1.04        50    1.31                                     0.75    1.56      1:2.08        42    1.18                                     0.38    1.56      1:4.10        36    1.18                                     0.19    1.56      1:8.21        32    1.14                                     6       0.78      7.69:1        90    0.79*                                    3       0.78      3.85:1        72    0.85*                                    1.5     0.78      1.92:1        47    1.27                                     0.75    0.78      1:1.04        31    1.46                                     0.38    0.78      1:2.05        24    1.31                                     0.19    0.78      1:4.10        21    1.10                                     ______________________________________                                          .sup.1 Product containing 40% actives DIMPS                                    .sup.2 Product containing 80% actives TCMTB                              

Asterisks in the SI column indicate synergistic combinations in accordance with the Kull method supra.

In the preceding tables, for all combinations tested, differences seen between the replicates are due to normal experimental variance.

In accordance with the preceding tables, unexpected results occurred more frequently within the following product ratios:

    ______________________________________                                                           From about                                                   ______________________________________                                         DIMPS to BNPD       1:1600 to 1:6.25                                           DIMPS to PEO        1:211,000 to 1:417                                         DIMPS to TCMTB      1:79.0 to 7.69:1                                           ______________________________________                                    

The individual products contain the following amounts of active biocidal components:

DIMPS: about 40%

BNPD: about 95%

TCMTB: about 80%

PEO: about 40%

Therefore, when based on the active biocidal component, unexpected results appear more frequently within the following ranges of active components:

    ______________________________________                                                           From about                                                   ______________________________________                                         DIMPS to BNPD       1:3800 to 1:14.8                                           DIMPS to PEO        1:211,000 to 1:417                                         DIMPS to TCMTB      1:158 to 3.85:1                                            ______________________________________                                    

At present, it is most preferred that commercial products embodying the invention comprise weight ratios of active components of about:

1:15 DIMPS:BNPD

1:500 DIMPS:PEO

1:1 DIMPS:TCMTB

While this invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modifications of this invention will be obvious to those skilled in the art. The appended claims and this invention generally should be construed to cover all such obvious forms and modifications which are within the true spirit and scope of the present invention. 

We claim:
 1. A method for controlling the growth of fungal microbes in an aqueous system which comprises adding to an infected aqueous system a synergistic fungicidally effective amount of the mixture of (a) diiodomethyl-p-tolylsulfone and (b) 2-(thiocyano-methyl thio) benzothiazole, the weight ratio of (a) to (b) being from about 1:158 to 3.85:1.
 2. The method as recited in claim 1 wherein said composition is added to said system in an amount of from about 0.1 to about 200 parts per million of said aqueous system.
 3. The method as recited in claim 1 wherein the weight ratio of (a) to (b) is about 1:1.
 4. The method as recited in claim 1 wherein said aqueous system comprises a cooling water system.
 5. The method as recited in claim 1 wherein said aqueous system comprises a pulping and papermaking system.
 6. The method as recited in claim 1 wherein said fungal microbes are of the Trichoderma viride variety. 